JavaScript Performance on GTK Linux Browsers

I've recently noticed that my system is sluggish on certain web pages which
incorporates lots of behavior with JavaScript. I've been running
Iceweasel from Debian's testing repositories for ages. I had heard some
mentions of lower memory usage and faster JavaScript in the upcoming 3.0
release of Firefox®/Iceweasel throughout the blogosphere.
In addition the developers of Epiphany have recently decided to use
WebKit as their default backend.

I desperately needed better JavaScript performance and decided to test the
stable 2.0 branch of Iceweasel against the latest beta version from the
3.0 branch together with the latest WebKit enabled Epiphany from the
Debian unstable repositories. Why not test Opera? Firstly Opera is
Qt and not GTK based -- a showstopper for me. Secondly Opera
is not open source software. Thirdly Opera does not natively
run on the x86-64 architecture.
Therefore the browser versions used for testing were as follows
(identified by their user User-Agent request header):

I decided to use John Resig's Dromaeo and WebKit's
SunSpider JavaScript performance test suites to benchmark the
performance of the selected browsers against each other. Remember
the wise words of Benjamin Disraeli:

There are three kinds of lies: lies, damned lies, and statistics.

The performance metrics presented here applies for my system, and my system
alone. There could be a myriad of factors contributing to the numbers I
received. To keep such factors to a minimum I rebooted my system before
staring the browser under testing, and then restarted my system again before
testing the next browser. In addition I blasted away any profiles, running the
browsers vanilla without any cache, history, cookies, nor extensions.

I started writing a script with Hpricot and ghcartrb to generate
some nice detailed charts of the differences between the browsers. But when I
found myself writing code like this:

Based on these observations it's not hard to see that there have been major
improvements from the 2.0 releases to the forthcoming 3.0 release of
Iceweasel with regards to JavaScript performance. The WebKit enabled
Epiphany browser is on par with Iceweasel 3.0 in the Dromaeo test suite
while it seems to be marginally faster than Iceweasel 3.0 in the
SunSpider test suite.

The differences between Iceweasel 3.0 and Epiphany does not seem to be
sufficient for switching. Epiphany does seem to be a bit more light weight
and is delivering everything I need in a browser. The only thing holding me
back is the Vimperator extension for Iceweasel. I simply can't live
without vi keybindings in my browser now that I've gotten used to it.
I'll adopt the 3.0 branch of Iceweasel if it proves to be stable over some
more prolonged use.